MailChimp supports triggers of “When A Member Has Been Added To A List” & “When A New List Is Created”; for anything else you need to use a webhook.
While MailChimp has documentation here, it misses one important step to get it working with Power Automate; and that is that when you save your configuration in MailChimp it performs a GET request to check the validity of the URL you’ve provided. After this it only uses POST.
To set this up with Power Automate first create a trigger using “When a HTTP request is received” and under Show Advanced Options set the Method to GET.
Add an Action “Initialize Variable”, set its Type to Object and Value to “Body” of the trigger “When an HTTP request is received”
At this point you can save the Flow and a URL is generated in the initial trigger…
Copy this URL and head on over to your MailChimp dashboard.
Select your Audience and in the dropdown on the right hand side go to Settings.
Down the bottom select Webhooks, and Create New Webhook.
Paste the copied URL from above into the “Callback URL” field, select what Updates you want, and hit Save.
At this point you can return to your flow and remove GET from the Method under Show Advanced Options and you should be able to test it out.
Just keep in mind that if you go to modify the MailChimp webhook at any time you’ll have to set the method back to GET temporarily while MailChimp verifies the supplied URL again.
I then grab the email address from the provided $formdata using…
Hope this helps someone.